This invention relates in general to bicycles, and more particularly to bicycle steerer tubes.
A conventional bicycle (a mountain bike is shown at 100 in FIG. 1) is steered by varying the plane of its front wheel 102 out of a plane of travel P, which is aligned with the running direction of the bicycle. This is done by linking the front wheel 102 to a rider-operated handlebar 104. The front wheel 102 is rotatably suspended between left and right tubes 106, 108 of a fork indicated generally at 110. The left and right fork tubes 106, 108 are joined, either in solid fashion or by shock absorbing apparatus, to a fork crown 112 positioned upward from the front wheel.
Referring to FIGS. 1 and 2, a steerer tube 200 has its lower end 202 affixed to the fork crown 112 and is disposed along an upwardly and usually rearwardly extending steering axis X. Axis X is within the plane of travel P. The steerer tube 200 is inserted into a coaxial head tube 204 that is part of a bicycle frame 206. Bearings are mounted between the steerer tube 200 and the head tube 204 to permit the free rotation of the steerer tube 200 relative to the head tube 204. The handlebar 104 is affixed in some fashion (as by a star nut, not shown) to an upper end 212 of the steerer tube, and permits the rider to impart torque to the steerer tube 200, the fork 110 and the front wheel 102, which in response rotate around the steering axis X as a unit. Thus, the rider may steer the bicycle 100 right or left as desired.
Many conventional steerer tubes are circularly cylindrical. A perfectly cylindrically circular steerer tube, having a uniform wall thickness, will exhibit a uniform stiffness longitudinally, or fore-and-aft and in alignment with plane of travel P, and laterally, or side-to-side and perpendicular to plane of travel P and axis X. But uniformly thick and stiff steerer tubes do not take into account the differences in loads on the steerer tube and stability, comfort and steering requirements.